1. Field of the Invention
The present invention relates to a spin valve sensor with dual self-pinned AP pinned layer structures wherein magnetic moments of AP pinned layers in the AP pinned layer structures can be oriented in-phase with respect to one another by an exterior magnetic field.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has write and read heads, a suspension arm above the rotating disk and an actuator arm. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the actuator arm swings the suspension arm to place the write and read heads over selected circular tracks on the rotating disk where field signals are written and read by the write and read heads. The write and read heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a spin valve sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90xc2x0 to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the rotating disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is preferably parallel to the ABS, is when the sense current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. An increase in scattering of conduction electrons increases the resistance of the spin valve sensor and a decrease in scattering of the conduction electrons decreases the resistance of the spin valve sensor. Changes in resistance of the spin valve sensor is a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layers. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
The sensitivity of the spin valve sensor is quantified as magnetoresistance or magnetoresistive coefficient dr/R where dr is the change in resistance of the spin valve sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the spin valve sensor at minimum resistance. Because of the high magnetoresistance of a spin valve sensor it is sometimes referred to as a giant magnetoresistive (GMR) sensor.
A dual spin valve sensor may be employed for increasing the magnetoresistive coefficient dr/R of a read head. In a dual spin valve sensor first and second pinned layer structures are employed with a first spacer layer between the first pinned layer structure and the free layer and a second spacer layer between the second pinned structure and the free layer. With this arrangement the spin valve effect is additive on each side of the free layer to increase the magnetoresistive coefficient dr/R of the read head. In order to reduce demagnetizing fields HD from the first and second pinned layers on the free layer, each of the pinned layers may be an antiparallel (AP) pinned layer structure. The first AP pinned layer structure has an antiparallel coupling (APC) layer which is located between ferromagnetic first and second AP pinned layers (AP1) and (AP2) and the second AP pinned layer structure has another antiparallel coupling layer which is located between another first and second AP pinned layers (AP1) and (AP2). The AP pinned layers of each AP pinned layer structure have magnetic moments which are antiparallel with respect to one another because of a strong antiferromagnetic coupling therebetween. The AP pinned layer structure is fully described in commonly assigned U.S. Pat. No. 5,465,185 which is incorporated by reference herein. Because of the partial flux closure between the AP pinned layers of each first and second AP pinned layer structures, each AP pinned layer structure exerts a small demagnetizing field on the free layer.
In a dual spin valve sensor, where the pinned layer structures are AP pinned layer structures, the first AP pinned layer of the first AP pinned layer structure interfaces the first spacer layer and the first AP pinned layer of the second AP pinned layer structure interfaces the second spacer layer. In order for the aforementioned spin valve effect to be additive on each side of the free layer it is important that the AP pinned layer structures be in-phase with respect to one another. This occurs when the magnetic moments of the first AP pinned layers of the first and second AP pinned layer structures are oriented perpendicular to the ABS and parallel with respect to one another. Accordingly, when a signal field from a rotating magnetic disk rotates the free layer structure the change in resistance of the sensor due to the magnetoresistive coefficient will be additive to increase the signal output of the read head.
The present invention provides a spin valve sensor with dual self-pinned AP pinned layer structures wherein magnetic moments of the AP pinned layers within the AP pinned layer structures can be set in-phase by an exterior magnetic field. In one embodiment of the invention this is accomplished by providing each of the first AP pinned layers of the first and second AP pinned layer structures with a magnetic thickness which is greater than the magnetic thickness of either of the second AP pinned layers of the first and second AP pinned layer structures. In another embodiment of the invention this is accomplished by providing each of the first AP pinned layers of the first and second AP pinned layer structures with a magnetic thickness which is less than the magnetic thickness of either of the second AP pinned layers of the first and second AP pinned layer structures. In either embodiment an exterior magnetic field, which is oriented perpendicular to the ABS, will set the magnetic moments of the thicker AP pinned layers in the same direction which will cause the magnetic moments of the thinner AP pinned layers to be oriented antiparallel thereto. Previously, the orientation of the magnetic moments of the AP pinned layers of the first and second AP pinned layer structures were determined by the orientations of magnetic spins of first and second pining layers which were exchange coupled to the first and second AP pinned layer structures respectively.
Another aspect of the invention is to provide a seed layer structure wherein a bottom portion of the seed layer structure is sputter etched before depositing a top platinum manganese (PtMn) layer of the seed layer structure thereon. Still another aspect of the invention provides a method wherein: (1) the easy axes of the AP pinned layers of the first and second AP pinned layer structures are set perpendicular to the ABS by a first magnetic field; (2) orienting the magnetic moments of the AP pinned layers in-phase and perpendicular to the ABS, as discussed hereinabove, by a second magnetic field; and (3) longitudinally setting the magnetic moments of first and second hard bias layers which longitudinally bias the free layer structure, by a third magnetic field oriented parallel to the ABS and parallel to major planes of the AP pinned layers.
An object of the present invention is to provide a spin valve sensor with dual self-pinned AP pinned layer structures wherein magnetic moments of AP pinned layers within the AP pinned layer structures can be set in-phase by an exterior magnetic field.
Another object is to provide the aforementioned spin valve sensor wherein the self-pinning of the dual AP pinned layer structures is improved.
A further object is to provide a method of making the aforementioned spin valve sensor.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.